Circuit simulation is a critical aspect in the modern circuit design process. The design process is a highly interactive operation wherein the designer uses the simulator to explore the circuit. It is important that the iterative exploration process of circuit design be as efficient and as natural as possible. Some circuits, such as a network of resistors, act as a linear system and can be simulated using conventional approaches. Other circuits, such as an RF and microwave circuits, do not act as linear systems and are comparatively difficult to simulate due to their non-linear nature. One method devised to simulate circuits with non-linear components is harmonic balance analysis.
Historically, harmonic balance analysis was a mixed analysis technique that works by dividing a circuit that contains both linear and non-linear components into two subnetworks: a linear subnetwork that contains the linear circuit components and a non-linear subnetwork that contains the non-linear circuit components. The two subnetworks may be connected by one or more ports, e.g. P1, P2, PN, that correspond to the number of non-linear components. The linear subnetwork may then be solved using a frequency domain approach, while the non-linear subnetwork may be solved using a time-domain approach. After initial results for the two subnetworks are determined, the results are combined over multiple error reducing iterations. Another conventional approach is shown in FIG. 3 and discussed in detail below. While these conventional approaches may yield more accurate results than previous methods, they still have several drawbacks.
For instance, the accuracy of harmonic balance analysis is often dependent on the number of harmonics required to accurately model the non-linear components in the system. In circuits with highly non-linear components, the number of harmonics required can be significantly large. The large number of harmonics required to accurately simulate the circuit can cause problems with the noise floor, convergence (e.g. the ability to reach a steady state result), and processor/memory usage. For instance, in a circuit with one or more local oscillators (LO) and frequency divider pairs, conventional harmonic balance approaches have difficulty converging the total system to the steady state result because these circuits are extremely nonlinear and difficulty to represent in a Fourier-series basis. In some cases, the system never converges and a result cannot be generated.
These issues are further compounded in multicarrier RF systems, such as LTE; where as the number of carriers increases, the number of independent frequencies (sometimes called “tones”) in the harmonic balance analysis also increased. Thus the amount of data that must be processed and stored for a single simulation can easily reach many terabytes. Further, given the large amounts of data that must be processed, the time required to output accurate results for multicarrier analysis often exceeds practical limitations.
As is evident, there is a need for an approach to simulate circuits with non-linear components, such as those found in multicarrier systems, in a way that maintains accuracy while reducing processing and memory consumption to practical levels.